The present invention relates to a braking pressure generator for slip-controlled brake systems of automotive vehicles comprising dynamic and static pressure fluid circuits. Pressure fluid is metered into the fluid circuits during braking with slip control from the dynamic circuits by way of a prechamber which during braking without slip control is connected with a pressure compensating reservoir and from which the dynamically introduced pressure fluid is fed by way of check valves. The check valve can be designed, for example, as valves in the master cylinder collar in the static brake circuits. The braking pressure generator includes a differential pressure pilot valve including a piston which under the action of the differential pressure is axially slidable within a cylinder and which upon exceeding a differential pressure threshold actuates an alarm switch.
In a known braking pressure generator of the type to compare the pressure proportional to the pedal force introduced into the booster chamber of a hydraulic brake force booster is compared with the pressure in a static brake circuit and by means of a differential pressure pilot valve. Upon starting of the slip control pressure fluid is metered from the dynamic into the static circuit. The braking pressure generator comprises the combination of a hydraulic brake force booster with a master cylinder onto which the booster pressure acts. As long as there is a pressure balance, the piston is kept in an intermediate position. If the differential pressure passes a predetermined differential pressure threshold in either direction, this indicates an error in the braking pressure generator or the elements connected thereto, which causes the brake slip control to be partially switched off or entirely by way of a signal triggered by the differential pressure pilot valve. This is described in German patent document DE-OS No. 32 32 052 the U.S. counterpart application which issued as U.S. Pat. No. 4,555,144.
The disadvantage of this known system is that a defect of the main valve controlling the dynamic flow of pressure into the static circuit is not recognizable. To avoid this disadvantage the differential pressure pilot valve is connected to a prechamber located downstream of the main valve in the dynamic flow path instead of the booster chamber. The disadvantage in turn is that the functioning of the valve is no longer checked in every braking action, but only in slip-controlled braking actions. As a consequence, an error can remain undetected for a long period of time.
Therefore, the object of the present invention is to eliminate the disadvantages described and to insert and switch the differential pressure pilot valve hydraulically and electrically in such a way that the valve is operated constantly. That is, during braking actions with slip control as well as without slip control, and any error in the braking pressure generator or in the monitoring components is immediately recognized and signalized so as to ensure that by partial or complete cutoff of the brake slip control at least a braking with limited slip control or a braking without slip control remains possible.